Irrigation systems that deliver water, often containing plant nutrients, pesticides and medications, to plants via networks of irrigation pipes are very well known. In many such irrigation networks, water from the pipes is delivered to the plants by drippers that are coupled to the pipes at appropriate locations along their lengths. In many instances, the drippers are configured to deliver a substantially same regulated amount of water to a region substantially independent of water pressure in the pipe at the point at which they are coupled to the pipe. In general, the irrigation pipes are formed from a plastic and the drippers comprise a suitable formed “coupling nipple” for connecting the drippers to the irrigation pipes. A dripper is connected to an irrigation pipe by forming a hole in the pipe and pushing its coupling nipple through the hole. The coupling nipple is formed so that after it is pushed through the hole it fits snuggly in the hole and seals the dripper to the pipe to prevent seepage of water from the hole. For many irrigation systems and/or drippers the hole is formed using a specially designed “punch tool”.
To simplify connecting drippers to irrigation pipes, some drippers are formed with a self-puncturing coupling nipple having a sharp point so that the dripper may be coupled to an irrigation pipe by pressing its coupling nipple to the pipe with sufficient pressure so that the coupling nipple punctures and penetrates the pipe wall. The coupling nipple is shaped so that once it punctures and penetrates the irrigation pipe wall, it remains securely lodged in the hole that it formed. Self-puncturing drippers are used with irrigation pipes whose walls are sufficiently soft and pliable so that a self-puncturing dripper may be coupled to an irrigation pipe with the application of a moderate level of, generally manual, force.
Self-puncturing drippers are conventionally formed from a relatively hard plastic so that the coupling nipple maintains sufficient rigidity and sharpness to puncture an irrigation pipe. However, the hard plastics, for example polyacetal (POM), typically used to produce self-puncturing drippers are generally expensive and are relatively susceptible to damage from prolonged contact with many of the plant nutrients, pesticides and medications that are comprised in water delivered to plants by an irrigation system.
Often, when setting up an irrigation system, irrigation pipes of different lengths have to be connected to provide a desired configuration of pipes and drippers. Press-fit pipe couplers are frequently used to couple the pipes. A press-fit pipe coupler usually comprises a tube having formed on its outer surface annular “gripping” ribs that are shaped with a “gripping” edge. To join two irrigation pipes, each end of the tube is pressed into an end of a different one of the pipes. The radius of the tube and a distance at which the gripping edges are located from the tube surface are such that after an end of the tube is pressed into a pipe end, the tube lodges snuggly in the pipe with the gripping edge of at least one rib “biting” into the inner wall of the pipe.
Some press-fit couplers, which are used in low pressure irrigation systems, are formed by injection molding from relatively soft inexpensive plastics. They are not generally convenient for use in high pressure systems because their “soft plastic” gripping ribs do not provide a secure purchase on the inside walls of irrigation pipes into which they are inserted. If used in high pressure irrigation systems, soft plastic press-fit couplers are generally connected to irrigation pipes using external clamps or rings that are tightened about the pipes to squeeze the pipe walls to the couplers to assure secure connection of the couplers to the pipes. To make press-fit pipe couplers that generally do not require clamping accessories to provide a secure fit of the couplers to pipes, press-fit pipe couplers are injection-molded from an appropriately hard plastic so that their gripping ribs have sufficient rigidity to maintain their bite on walls of irrigation pipe they couple and prevent the pipes from separating during normal use. As in the case of the drippers, the hard plastics used to form press-fit pipe couplers are relatively expensive and generally susceptible to damage from prolonged contact with many of the materials that are added to water used to irrigate plants.
A generally preferred plastic used for irrigation applications and products, and from which drippers are usually formed and injection-molding equipment used to produce the dripper adapted to mold, is polypropylene. Polypropylene is relatively cheap, abundant and resistant to damage by nutrients and other materials carried by water delivered to plants by irrigation systems. However, polypropylene is a relatively soft plastic and is not suitable for forming self-puncturing coupling nipples that are required to maintain a sharp, rigid point in order to puncture the wall of an irrigation pipe or for forming press-fit pipe couplers that have to maintain hard gripping edges that maintain their shape.